1. Field of the Invention
The present invention relates to an image forming apparatus and its control method applicable to an image forming apparatus such as electrophotographic or electrostatic copiers and printers.
2. Description of the Related Art
An outline of an entire configuration of a laser printer as an image forming apparatus will be described with reference to FIG. 1.
As shown in FIG. 1, the laser printer forms electrostatic latent images in an image forming section according to image light produced in response to image signals sent from a control section not shown, and forms visible color images by the development of the electrostatic latent images and by the superimposition transfer of the visible images. The visible color images are transferred onto a sheet (that is, recording medium) 2, and is fused on the sheet 2. The image forming section has photosensitive bodies (5Y, 5M, 5C, 5K) provided for individual stations juxtaposed by the number of development colors (four colors); injection charging means (7Y, 7M, 7C, 7K) as primary charging means; and developing means (8Y, 8M, 8C, 8K). The image forming section further includes toner cartridges (11Y, 11M, 11C, 11K), an intermediate transfer body 12, a paper feed section 1, a transfer section and a fusing section 13. Here Y designates yellow of the development colors, M designates magenta of the development colors, C designates cyan of the development colors, and K designates black of the development colors.
The photosensitive bodies (5Y, 5M, 5C, 5K), injection charging means (7Y, 7M, 7C, 7K) as the primary charging means, and the developing means (8Y, 8M, 8C, 8K) are mounted on process cartridges (22Y, 22M, 22C, 22K) which are detachably installed in the main body of the image forming apparatus.
The photosensitive drums (photosensitive bodies) 5Y, 5M, 5C and 5K, each of which is formed by applying an organic photoconductive layer on the outer surface of an aluminum cylinder, are rotated by a driving force transferred from a driving motor not shown. The driving motor causes the photosensitive drums 5Y, 5M, 5C and 5K to rotate counterclockwise in response to the image forming operation. The exposure light beams to the photosensitive drums 5Y, 5M, 5C and 5K are sent from scanners 10Y, 10M, 10C and 10K, and are selectively exposed on the surfaces of the photosensitive drums 5Y, 5M, 5C and 5K so as to form the electrostatic latent images.
The primary charging means has four injection charging units 7Y, 7M, 7C and 7K for charging the photosensitive bodies of yellow (Y), magenta (M), cyan (C) and black (K) for the stations, respectively. The injection charging units include sleeves 7YS, 7MS, 7CS, and 7KS, respectively.
The developing means includes four developing units 8Y, 8M, 8C and 8K for developing the yellow (Y), magenta (M), cyan (C) and black (K) at the individual stations to make the electrostatic latent images visible, respectively. The developing units have sleeves 8YS, 8MS, 8CS and 8CK, and are mounted detachably.
The intermediate transfer body 12, which makes contact with the photosensitive drums 5Y, 5M, 5C and 5K and rotates clockwise when forming the color image, rotates in conjunction with the rotation of the photosensitive drums 5Y, 5M, 5C and 5K, and receives the transfer of the visible images. In addition, the intermediate transfer body 12 makes contact with a transfer roller 9, which will be described later, when forming the image, and pinches and transports the sheet 2, thereby carrying out the superimposition transfer of the visible color images on the intermediate transfer body 12 to the sheet 2.
The transfer roller 9 is placed at the position 9a to make contact with the intermediate transfer body during the superimposition transfer of the visible color images on the intermediate transfer body 12 to the sheet, but is separated therefrom to the position 9b once the printing processing is completed. In other words, the transfer roller 9 moves in the direction of the arrow in FIG. 1 to make contact with or separation from the intermediate transfer body 12.
The fusing section 13, which fuses the transferred visible color images with conveying the sheet 2, includes a fusing roller 14 for heating the sheet 2 and a press roller 15 for pressing the sheet 2 on the fusing roller 14. The fusing roller 14 and press roller 15 are made hollow to include heaters 16 and 17 in the inside, respectively. Thus, the sheet 2 holding the visible color images is conveyed by the fusing roller 14 and press roller 15, and the toners are fused on its surface by imposing heat and pressure. After the visible image fusing, the sheet 2 is output to a paper output section, and the image forming operation is completed.
The printer controls the transportation of the sheet with a lower transport sensor A 23, an upper transport sensor A 24, a lower transport sensor B 25, an upper transport sensor B 26, a registration sensor 19, a pre-fusing sensor 27, a fused paper output sensor 20, and a paper output sensor 28 on the sheet transport path. In addition, at the paper feed slot of a paper feed section (cassette) 1, a sensor (not shown) is provided for detecting the presence and absence of the sheet in the paper feed section 1.
A cleaning means 21 cleans the toners left on the photosensitive drums 5Y, 5M, 5C and 5K and on the intermediate transfer body 12. Through the cleaning, discarded toners after transferring the visible images, which are formed on the photosensitive drums 5Y, 5M, 5C and 5K with the toners, onto the intermediate transfer body 12 are stored in a cleaner container. In addition, through the cleaning, the discarded toners after transferring the visible color images with the four colors, which are formed on the intermediate transfer body 9, onto the sheet 2 are stored in the cleaner container.
FIG. 2 is a block diagram showing a system configuration of an image forming apparatus. A controller section 201 can communicate with a host computer 200 and an engine control section 203. The controller section 201 receives image information and a print instruction from the host computer 200. The controller section 201 analyzes the image information received and converts it to bit data, and delivers for each sheet a print reservation command, a print start command, and a video signal to the engine control section 203 via a video interface 210.
The engine control section 203 has a CPU 211 for receiving the command and data sent from the controller section 201 via the video interface 210, and for instructing operation processing for forming an image. The engine control section 203 further includes an image processor 212 as a circuit for processing the image data to be printed, and an image control section 213 for carrying out read control of the data processed by the image processor. The engine control section 203 further includes a fusing control section 214 for controlling the fusing temperature of the fusing section 13, and a sheet transport section 215 (corresponding to a plurality of pairs of transport rollers of FIG. 1) for conveying a sheet through the image forming apparatus. The engine control section 203 further includes a drive control section 216 for controlling driving of a motor (not shown) for driving the sheet transport section 215, and a duplex control section 217 for detecting transport conditions of the sheet in a duplexer, and for controlling the transport operation. In addition, the CPU 211 controls the various sections constituting the engine according to control procedures (including the control procedure shown in FIG. 3) in a ROM not shown.
The controller section 201 sends a print reservation command to the engine control section 203 in response to the print instruction from the host computer 200, and delivers a print start command to the engine control section 203 at a print enabled timing. In this case, according to the instructions from the host computer 200, the controller section 201 sends to the paper output option control section 202 an instruction about the usage of the paper output control option, and to a paper feed option control section 204 an instruction about the usage of the paper feed control option.
The engine control section 203 makes preparations for printing in accordance with the sequence of print reservation commands from the controller section 201, and waits for a print start command from the controller section 201. Receiving the print instruction, the engine control section 203 supplies the controller section 201 with a /TOP signal that gives a reference timing of outputting the video signal, and starts the print operation in response to the print reservation command. In addition, the engine control section 203 outputs a /TOPR signal that gives a timing of paper refeeding of the sheet waiting at the registration roller. The controller section 201 issues a paper refeeding instruction to a paper feed option input apparatus via a paper feed option control section 204 at the time when the /TOPR signal becomes “true”.
FIG. 3 is a flowchart illustrating a print operation of the engine control section 203. Receiving the print reservation command, the engine control, section 203 waits for receiving the print start command (501), and carries out preprocessing for the print operation (called a “pre-rotation sequence” from now on) (502). After completing the pre-rotation sequence, the engine control section 203 outputs the /TOP signal, and starts the print operation in response to the print reservation command of a first sheet (503). Unless the engine control section 203 receives the next print reservation command by the next print operation start timing (called “normal print start timing”) (505), it advances the processing to step 509 to maintain the throughput. At step 509, the engine control section 203 carries out post-processing of the print operation (called a “post-rotation sequence” from now on), and completes the print operation. When the engine control section 203 has received the print reservation command and the print start command for the print reservation command by the next normal print start timing, it starts the print operation of a second sheet following the first sheet (506 and 503). When the engine control section 203 has received the print reservation command but not the print start command by the next normal print start timing, it carries out the post-rotation sequence and enters a print start command waiting state (507 and 508) to wait for receiving the print start command. Receiving the print start command, the engine control section 203 starts the pre-rotation sequence (502).
FIG. 4 illustrates a communication sequence up to starting the duplex printing of a fourth sheet with carrying out alternate paper feed from the paper feed section 1 and the duplexer. The controller section 201 sends to the engine control section 203 a reservation command with a reservation ID=1 for feeding paper from the paper feed section 1 and for outputting paper to the duplexer at 311; and sends a reservation command with a reservation ID=2 for feeding paper from the paper feed section 1 and for outputting paper to the duplexer at 312. At 313, the controller section 201 sends a reservation command with a reservation ID=1 for feeding paper from the duplexer and for outputting paper to a paper output section outside the apparatus. These operation steps are performed repeatedly for the rest of the reservation IDs (314, 315, 316, 317 and 318). Subsequently, the controller section 201 instructs the engine control section 203 to start printing for the reserved ID in response to the reservation command at 319, and the engine starts the print operation. The engine control section 203, after receiving the print start command, supplies the controller section 201 of the image forming sequence with a /TOP signal and /TOPR signal (320 and 321) to form an image. On the other hand, the controller section 201 outputs a video signal in synchronization with the /TOP signal, and outputs the print start command for the next reservation ID. Incidentally, carrying out paper feed from the paper feed section 1 and from the duplexer alternately with placing a single standby sheet at the duplexer as illustrated by the reservation commands from 311 to 318 is referred to as “two-sheet alternate duplex” from now on.
FIG. 5 shows an image forming sequence for forming an image according to the communication sequence of the duplex print in FIG. 4. In the duplex print below, as for a sheet that is fed from the cassette and output to the duplexer, its surface on which printing is made first is called a “first surface”, and its opposite surface on which printing is made while the sheet is fed from the duplexer and output to the outside of the image forming apparatus is called a “second surface”. Receiving the print start command (print ID=1) associated with the print reservation command of the first surface of the first sheet, the engine control section 203 starts the pre-rotation sequence. After completing the pre-rotation sequence, the engine control section 203 outputs the /TOP signal (100-1-S) to start the print operation of the first sheet, and transports the sheet from the cassette to the duplexer (101-1-S). In synchronization with the /TOP signal, the controller section 201 supplies the video data to the engine control section 203 to start forming the image. The engine control section 203 carries out with the registration sensor 19 the timing adjustment between the sheet fed from the cassette and the image transferred onto the intermediate transfer body by the image forming section. By performing the timing adjustment, the engine control section 203 outputs the /TOPR signal, and refeeds the sheet to transfer the image onto the sheet (102-1-S). The image transferred onto the sheet undergoes heat fusing by the fusing section 13, and passes by the fused paper output sensor 20. Thus, the image formation on the first surface of the first sheet is completed (103-1-S).
Likewise, receiving the print start command (print ID=2) associated with the print reservation command of the first surface of the second sheet, the engine control section 203 outputs the /TOP signal (100-2-S) to start the print operation of the first surface of the second sheet. Thus, the sheet is transported from the cassette to the duplexer (101-2-S), and the /TOPR signal is output (102-2-S). Subsequently, the fusing section 13 carries out the heat fusing of the image completely transferred on the sheet. The sheet passes by the fused paper output sensor 20, and the image formation on first surface of the second sheet is completed (103-2-S).
Next, when receiving the print start command (print ID=1) associated with the print reservation command of the second surface of the first sheet, the engine control section 203 outputs the /TOP signal (100-1-D) to start the print operation of the second surface of the first sheet. Thus, the sheet is transported from the duplexer (101-1-D), and the /TOPR signal is output (102-1-D). Subsequently, the fusing section 13 carries out the heat fusing of the image completely transferred on the sheet. The sheet passes by the fused paper output sensor 20, and the image formation on the second surface of the first sheet is completed (103-1-D). The sheet whose first and second surfaces both undergo the image formation passes by the paper output sensor 28, and is output to the outside of the image forming apparatus. The foregoing operation is repeated for the four sheets, and the post-rotation sequence is carried out again after completing all the image formation, followed by the waiting state of the print start command.
FIG. 6 illustrates an image forming sequence when the sheet in the paper feed section 1 has run out at the fourth sheet while carrying out the image forming sequence described in connection with FIG. 5 according to the communication sequence up to the start of the duplex print of the fourth sheet with performing alternate paper feed from the paper feed section 1 and from the duplexer of FIG. 4. In this case, the printing cannot be continued. Although the engine control section 203 outputs the /TOP signal (100-4-S) of the first surface of the fourth sheet and continues the image formation of the second surface of the first sheet, the fourth sheet has run out. Thus, no sheet can be transported from the cassette to the duplexer (101-4-S). When the sheet in the cassette has run out, the sensor at the paper feed slot of the paper feed section 1 detects the paper-out, and notifies the engine control section 203. Thus, the engine control section 203 sets the sheet presence or absence status at a paper-out. In addition, since the paper-out occurs, the engine control section 203 informs the controller section 201 of an occurrence of a misprint because of the paper-out (110). When the paper-out occurs, the engine control section 203 continues the image forming operation up to the second surface of the second sheet. In other words, the engine control section 203 notifies the controller section 201 through a sheet transport status that the sheet transportation is halted at the time when the second surface of the second sheet has passed by the fused paper output sensor 20, and is output to the outside of the image forming apparatus (103-2-D).
When the misprint has occurred in the engine, and the sheet transport status of the engine becomes not-in-transit, the controller section 201 determines the print ID necessary for the recovery (reprint) as follows. Specifically, the controller section 201 determines the print ID necessary for the recovery (reprint) by receiving from the engine control section 203 the reservation ID registered already, the ID associated with the paper feed from the paper feed section, and the ID with which the print has already started. In the example of FIG. 6, a decision is made that the retransmission of the third and fourth sheets is necessary from the reservation ID, in-paper-feed ID and in-printing ID for the print ID as shown in FIG. 7. The engine control section 203 executes a misprint release sequence in response to a misprint release command from the controller section 201.
As for a configuration for controlling the image forming operation by assigning the IDs, Japanese patent application laid-open No. 2001-088496 describes it.
In the conventional example, the image forming operation is completed at the time when the paper-out is detected, and the controller section 201 is informed of the misprint due to the paper-out, and when the image formation of the first and second surfaces of the print IDs corresponding to the /TOP signals output up to that time has been completed. Then, the engine control section 203 sets the sheet transport status at the not-in-transit, and waits for the misprint release from the controller section 201. In this case, since a residual sheet having its one side printed remain in the duplexer, the processing is necessary for outputting the single-side printed residual sheet within the image forming apparatus after the misprint release. In addition, the print IDs for the single-side printed sheets are to be subjected to the recovery.
This will be described in more detail by way of example of FIG. 6. Since the fourth sheet undergoes the paper-out misprint, when the image formation of the second surface of the second sheet, which has the print ID previous to the single side (first surface) of the fourth sheet, has been completed, the sheet transport status is set at not-in-transit. At that time, since the single-side printed third sheet remains in the duplexer, the third sheet is to be output to the outside of the apparatus in the condition in which only its single side is printed. Accordingly, as for the third sheet which is a sheet previous to the paper-out decision and whose single side has already been printed, the controller section 201 must retransmit the reservation command to carry out paper feed and single side print again for the recovery.
In other words, since the third sheet is output to the outside of the apparatus without passing through the duplex printing, the third sheet with its single side printed goes to waste.